Weak Signal from Airport Extreme

I have an Airport Extreme that is probably 5 years old or more. It has always worked well around my home with various laptops. The signal strength seems to be weakening. A computer right next to it has great signal strength, but one just one floor up has a weak signal, which never used to be. I often get a better connection tying into one of my neighbors who have unsecured wireless.

Does Airport lose signal strength as it ages? Is there something that I can do to refresh it?

Thanks,
Dave